1. Field of the Art
The present invention relates to a titanium-containing solid catalyst component for polymerization of .alpha.-olefins and a catalyst containing this catalyst component.
More particularly, the present invention relates to production of .alpha.-olefin polymers wherein it is made possible to obtain a polyolefin having a broad molecular weight distribution in a high yield by Ziegler polymerization using a specific titanium-containing solid catalyst component. Especially in case of polymerization of a monomer composed mainly of propylene, the present invention makes it possible to prepare a homopolymer or copolymer of propylene having a high rigidity and an excellent moldability under stable conditions industrially advantageously while reducing quantities of by-products.
2. Description of the Related Art
Many proposals have been made on solid catalyst components comprising titanium, magnesium and a halogen for preparing catalysts having a high activity and entailing little formation of by-products (see, for example, Japanese Examined Patent Publication No. 53-46799, Japanese Examined Patent Publication No. 56-16167, Japanese Unexamined Patent Publication No. 57-63310, Japanese Unexamined Patent Publication No. 58-32604 and Japanese Unexamined Patent Publication No. 60-130607), and according to these proposals, polyolefins having a high rigidity would be prepared at a high polymerization activity while entailing little formation of by-products, and the catalyst-removing step can be omitted and the preparation process can be simplified and rationalized. However, the molecular weight distribution of the polymer obtained would be narrower than that of the polymer obtained when the conventional titanium trichloride type catalyst is used, and therefore, the moldability would be impaired. Accordingly, improvements may be desired.
As the means for broadening the molecular weight distribution, there have been proposed treatment of catalyst components with heat or with a halogenating agent or an electron donor (see, for example, Japanese Unexamined Patent Publication No. 57-158204, Japanese Unexamined Patent Publication No. 59-56406, Japanese Unexamined Patent Publication No. 59-71309 and Japanese Unexamined Patent Publication No. 61-9406). However, the improving effect would be low and still insufficient, and the problems of reduction of the activity and increase of by-products may arise.
As another proposal, there can be mentioned the method in which the polymerization is continuously carried out in a plurality of reaction vessels or in multiple stages. A considerable improvement may be attained according to this method, but since a plurality of reaction vessels should be disposed, the problem of increase of the manufacturing cost arises. Therefore, development of a solid catalyst component capable of providing a polymer having a broad molecular weight distribution is desired.